The study is designed to compare medical therapy to surgical treatment in Parkinson's disease and to compare the benefits of two strategies for surgical treatment of Parkinson's disease. The study aims to enroll approximately 316 patients and will be conducted at six VA Parkinson's Diesease Research, Education and Clinical Care Centers (PADRECC's) and their affiliated academic medical centers. The joint participation of the VA and NINDS in this clinical trial will further the mission of both agencies in identifying optimal treatments for Parkinson's disease.